1. Field of the Invention
This invention relates to moisture-hardening varnishes based on derivatives of aliphatic diisocyanate mixtures.
2. Description of the Prior Art
Moisture-hardening resins based on aromatic polyisocyanates are known and can be produced in several manners. Unfortunately, these resins have a tendency to yellow upon exposure to sunlight.
Cyclic polyisocyanates, such as e.g. isophoronediisocyanate or methylene-bis-(4-cyclohexylisocyanate) are used for more demanding applications. However, the isocyanurate or the propanetriol prepolymer of these cyclic diisocyanates merely form hard, brittle films following moisture hardenings.
Based on cyclic polyisocyanates and, e.g., higher molecular polyols, NCO terminated adducts can be produced that provide hard or soft films, in each case elastic films, following moisture hardening. But the resins are inactive and must be activated with additions of, e.g., 0.1 to 0.2% tin catalysts, which limits the weathering resistance of the hardened films. The hardened films have excellent thermal and oxidative stability, but have no outstanding solvent stability.
Aliphatic polyisocyanates through their floating, NCO end groups introduce highly reactive moisture-hardening resins in the form of their isocyanurate or their propanetriol prepolymers, which, following hardening, form hard, elastic weather and solvent resistant films. However, their thermal and oxidative stability and compatibility with other products are problematical, as e.g., also with solvents and pigments which are present especially in cyclic polyisocyanate resins.
Hence, a need clearly continues to exist for moisture-hardening varnishes with both excellent thermal and oxidative stability, and resistance to solvent attack. Also, it is necessary for these moisture-hardening varnishes to have excellent storage stability.